The proposed work is directed towards obtaining biological data which will assist in the design of effective and safe neutron radiotherapy treatment plans. The specific aims are: (a) to study parameters which affect the RBE for late damage in normal tissues following fractionated irradiation, (b) to compare the RBE for late and early damage in normal tissue, (c) to determine the influence of time between exposures on recovery of injury leading to damage in several normal tissues.